Ink jet printing is a well-known technique by which printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves the technique of projecting a stream of ink droplets to a surface and controlling the direction of the stream electronically so that the droplets are caused to form the desired printed image on that surface. This technique of noncontact printing is well suited for application of characters onto a variety of surfaces including porous and non-porous surfaces.
Reviews of various aspects of ink jet printing can be found in these publications: Kuhn et al., Scientific American, April, 1979, 162-178; and Keeling, Phys. Technol., 12(5), 196-303 (1981). Various ink jet apparatuses are described in the following U.S. Pat. Nos. 3,060,429, 3,298,030, 3,373,437, 3,416,153, and 3,673,601.
In general, an ink jet composition must meet certain rigid requirements to be useful in ink jet printing operations. These relate to viscosity, resistivity, solubility, compatibility of components and wettability of the substrate. Further, the ink must be quick-drying and smear resistant, must be capable of passing through the ink jet nozzle without clogging, and must permit rapid cleanup of the machine components with minimum effort.
Water-based or aqueous jet inks have been in particular demand so that industry can meet the low VOC regulations and improve work place and environmental safety. Several aqueous jet ink compositions have been disclosed in the patent literature. For example, U.S. Pat. No. 5,207,825 discloses a jet ink composition which comprises an aqueous liquid vehicle, a colorant, and a polymeric additive which is a substituted bisphenol A derivative.
U.S. Pat. No. 5,080,716 discloses a jet ink composition comprising a recording agent, a liquid medium capable of dissolving or dispersing the recording agent, and a substituted benzene or toluene sulfonamide compound.
U.S. Pat. No. 5,254,158 discloses an ink composition which comprises an aqueous liquid vehicle, a colorant, and an additive selected from the group consisting of amine alkoxylates, sorbitan monoester alkoxylates, alkylene oxide adducts of glycerin, and mixtures thereof.
U.S. Pat. No. 5,316,575, having the same assignee as the present application, discloses an ink composition suitable for ink jet printing, comprising an aqueous resin solution and an organic pigment, wherein said ink composition is substantially free of volatile organic compounds.
U.S. Pat. No. 5,345,254 discloses a jet ink composition which is an emulsion or suspension of an organic phase in a water phase, the organic phase including at least one of oil and wax. In one embodiment, the organic phase is said to contain a colorant which may be a pigment or oil soluble dye, and at least one of oil and wax. When certain embodiments of this invention are employed in jet printing, the jet nozzle requires heating to prevent clogging by the wax particles.
U.S. Pat. No. 3,687,887 discloses an aqueous jet ink composition suitable for titling of film or photographic negatives, which is an aqueous system containing a dissolved styrene-maleic anhydride or polyvinyl acetate resin, glycol ethers, carbon black, and certain other additives.
Some of the previously known aqueous jet inks have certain drawbacks such as long drying times, poor adhesion to substrates as shown, for example, by poor finger nail scratch resistance and finger rub resistance, and poor wet adhesion, water fastness, and print quality. Various approaches have been proposed to overcome these drawbacks. For example, the drying time can be greatly reduced through the use of a drying device such as an air knife or an IR lamp. Further, water fastness can be improved by the use of pigments instead of dyes. However, it has been a great challenge to develop a water based jet ink that offers images having good rub and scratch resistance when printed on substrates such as glass, metal, and plastics, and particularly when printed on non-polar substrates such as polyolefins including halogenated polyolefins which are the most difficult substrates to print on.
Thus, there exists a need for aqueous jet ink compositions that can meet the low VOC regulations. There further exists a need for aqueous jet ink compositions that offer improved water fastness and improved adhesion to substrates. There also exists a need for aqueous jet ink compositions that offer images having good rub and scratch resistance such as finger nail scratch resistance and finger rub resistance, particularly when printed on non-polar substrates such as polyethylene, polypropylene, and tetrafluoroethylene.
These and other objects of the present invention will be apparent from the detailed description of the preferred embodiments of the invention set forth below.